POS0700 METABOLIC AND MORPHOLOGIC PET/MR FEATURES IN CRANIAL GIANT CELL ARTERITIS
Authors: P. Nienhuis, C. M. Sørensen, K. Keller, I. Hansen, E. Naeser, M. Nyhuus Bendix Rasch, E. Brouwer, R. Slart, A. Dias, A. Appelman, E. M. Hauge, L. C. Gormsen, B. Dalsgaard Nielsen
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Accurate and timely diagnosis is crucial for patients suspected of having cranial giant cell arteritis (C-GCA) as prompt treatment with high-dose glucocorticoids may prevent severe ischemic complications, such as vision loss. However, the use of high-dose glucocorticoids in patients without proven C-GCA should also be done with caution due to potential side effects. Currently, multiple diagnostic (imaging) tests are required to establish an accurate diagnosis as single tests lack sufficient diagnostic sensitivity. Next to ultrasonography, 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG-PET/CT) and Magnetic Resonance Imaging (MRI) are used in clinical practice but carry a significant risk of false negative results. Since FDG-PET imaging measures metabolic activity, while MRI demonstrates morphological changes, combining these modalities may result in a composite hybrid diagnostic test with higher diagnostic accuracy. <h3>Objectives</h3> To describe the metabolic and morphologic imaging features of FDG-PET/MR in patients with diagnosed C-GCA. <h3>Methods</h3> Patients diagnosed with new-onset C-GCA underwent FDG-PET/CT and FDG-PET/ MR at 1 and 2 hours after FDG administration, respectively. Patients who had received treatment with glucocorticoids for more than 3 days prior to imaging were excluded from participating. Diagnosis of C-GCA was determined based on clinical information and the results from ultrasonography and FDG-PET/CT. On FDG-PET/MR imaging, thirteen arteries were evaluated bilaterally. Time-of-Flight (TOF) MR angiography was used to detect arterial stenoses or occlusions which were visually graded as either absent or present. To assess vessel wall thickness, T1-weighted contrast-enhanced (T1WCE) MRI images were visually graded on a scale of 0-3, with 0 indicating no mural enhancement or thickening, 1 indicating slight mural enhancement but no thickening, 2 indicating significant mural enhancement and thickening, and 3 indicating mural and perivascular enhancement and thickening. FDG uptake was visually graded on a scale of 0-2, with 0 indicating no vascular uptake, 1 indicating uptake slightly above background, and 2 indicating uptake significantly above background. <h3>Results</h3> The study included 12 patients with new-onset C-GCA with a median age of 74 years (range 61-84 years), of which 9 were female. The mean C-reactive protein (CRP) concentration was 63.2 (SD 41.0) mg/L, and one patient was receiving daily 60 mg prednisolone at the time of imaging (Figure 1, patient 12). Cranial artery ultrasonography was positive in 9 patients, and FDG-PET/CT was positive in the cranial arteries in 10 patients. All patients had at least one positive artery on T1WCE MRI (score ≥ 2) and all but one patient showed at least one arterial stenosis or occlusion on TOF MR angiography. One patient without FDG uptake FDG-PET/MR did also not show any FDG uptake on FDG-PET/CT. Figure 1 shows a heatmap of (a) presence of stenoses/occlusions, (b) the vessel wall thickening score (0-3), (c) the FDG uptake score (0-2), and (d) the overlap of FDG-PET positivity (score ≥ 1), T1WCE MRI positivity (score ≥ 2), and TOF MR angiography positivity. Data for each patient (1 to 12) is shown for each map in rows and data for each artery (Right and Left) are shown in columns. Vessel wall thickening and FDG-uptake were most seen in the vertebral, maxillary, and occipital arteries. Stenosis was most observed in the maxillary arteries. TOF MRA, T1-weighed contrast-enhanced MRI, and FDG-PET/CT scores agreed in 60% of all arteries, however just 10% of all positive arteries were positive on all three modalities. Agreement was highest (74%) between FDG-PET/CT and T1WCE MRI. <h3>Conclusion</h3> The study found an overlap in morphologic and metabolic features in affected arteries in patients with C-GCA using hybrid FDG-PET/MR. However, it also revealed that these features can occur independently of each other. This suggests that the use of hybrid morphologic and metabolic imaging may provide complementary information, potentially increasing diagnostic accuracy for C-GCA. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.